This invention relates to a projection-type video display device for projecting images. A conventional projection-type video display device is equipped with a video display element such as a liquid crystal panel whose picture elements are arranged in a matrix, and a light source which irradiates the video element. The video display element modulates the light strength of every picture element light source according to the image signal. The image thus generated is magnified by a unit such as a projection lens to be projected on a screen.
Projection-type video display devices are often used by business users, for example, for presentations, by projecting images from a personal computer onto a screen. Accordingly, priority has been given to optical brightness and high-power light sources or highly efficient illumination optical systems have been developed to project images clearly, even in a well-lighted room.
Alternatively, rear-projection-type video devices are currently being marketed. These are equipped with an optical unit inside a cabinet, for projecting images onto the back of a screen placed in a predetermined position. The rear-projection-type display device is generally used for a home theater, to enjoy television or video images. This tends to create a demand for high-quality image, durable products. Projection-type video devices are designed to give priority consideration, not only to optical brightness for excellent color purity, color reproducibility, contrast, etc. but also to having a display screen with a long life. An example of a projection-type video device with high quality color purity is disclosed in JP-A-2001-92419, and a projection-type video device with high contrast is disclosed in JP-A-2002-131750.
The projection-type video display of the 92419 patent document above is designed to have improved color purity for every color by blocking yellow components of wavelengths of 570-590 nm from coming into the red light flux R or the green light flux G. However, achieving color balance when synthesizing a red image light beam Ri, a green image light beam Gi, and a blue image light beam Bi, which are finally modulated by the video display element, is not taken into consideration. In particular, a chromaticity problem of a white-displayed image is produced by synthesizing the red image light beam Ri, the green image light beam Gi and the blue image light beam Bi because the y-value is high at a position of vertical separation from a locus of a black body on the chromaticity coordinates, causing a greenish white hue.
Moreover, color preference tends to have changed lately, the bluish white of color temperature of 9800° K being increasingly favored just like a cathode-ray-tube-type television. In this system, however, a technique for heightening the color temperature of white is not disclosed, nor is the necessity for heightening the color temperature of the white display suggested.
On the other hand, the projection-type video device described in the 131750 patent document is designed to improve contrast by arranging an optical phase difference compensator between the respective R, G and B image display elements and an incidence-side polarizing plate. Color reproducibility, or the color temperature of white, however, is not taken into consideration in this device. Though contrast characteristics are improved, the problem of uneven color occurs in the black display because of the optical phase difference compensator. In the projection-type video display devices described in these patent documents, details relating to producing a long-life liquid crystal panel as a video display element are not considered.